The advantages of providing pacing therapies to the left side heart chambers and to both the right and left heart chambers are well established. For example, in four chamber pacing systems, multiple pacing leads, typically bipolar leads, are positioned for both pacing and sensing in or on the respective heart chambers. To provide left side pacing and sensing, leads are transvenously placed in the coronary sinus region, for example, in a vein such as the great vein or the left posterior ventricular (LPV) vein proximate the left ventricle of the heart. Such placement avoids the risks associated with implanting a lead directly within the left ventricle that can increase the potential for the formation of blood clots which, if dislodged, could cause a stroke.
FIG. 1 shows an example of a typical bipolar left side lead 10. The lead 10 includes a lead body 12 having a distal portion 14 and a proximal portion 16. The distal portion 14 may carry various combinations of pacing, sensing and/or defibrillation electrodes, all well-known in the art. In the specific example shown in FIG. 1, the distal portion of the lead includes a tip electrode 18 at the distal extremity of the lead body 12 for delivering electrical stimuli to selected tissue of the heart, a ring sensor electrode 20 positioned proximally of the tip electrode 18 and a shocking electrode 22 disposed proximally of the ring electrode 20. These electrodes are electrically connected to a connector assembly 24 at the proximal extremity of the lead body 12. Typically, the connector assembly 24 comprises a coaxial structure including a hollow or tubular connector pin 26 and a plurality of terminal contact rings 28. Further, as is well-known in the art, the connector assembly 24 may comprise a bifurcated or trifurcated structure depending upon the number and functions of the electrodes carried by the distal portion 14 of the lead body.
A lead such as that shown in FIG. 1, designed for placement in the coronary sinus region of the heart, will typically include an anchoring or fixation means 30. In the example under consideration, the fixation means 30 comprises one or more bends preformed along the distal portion of the lead body. As is known, with such a sinuous configuration, the bend or bends in the distal portion of the lead will press against the walls of the coronary vessel within which the distal portion of the lead is placed. The friction caused by such biasing tends to anchor or fix the distal portion of the lead body.
Presently, the distal portion of a medical lead such as that shown in FIG. 1 is maneuvered into position within a coronary vessel by means of a stylet and/or by means of a guide wire. In the latter case, an “over-the-wire” (OTW) placement technique is utilized. Such lead placement methods are well-known in the art.
The placement of a lead in the coronary sinus region is often difficult because of the extreme curvatures in the veins, their narrowness, anomalies in the vascular anatomy because of disease, and the number of veins that may communicate with the desired lead feed path. Stylets are often found to be too stiff to be easily steered within the tortuous vasculature of the coronary sinus region. Thus, a more common approach to the left side implantation of an intravenous lead is the use of a flexible guide wire over which the lead is slid to its destination. For this purpose, the lead body is typically provided with a tip electrode having a central aperture through which the guide wire can pass.
With reference to FIG. 2, there is shown a typical guide wire 40 in present use. The guide wire 40 comprises a thin, solid wire body 42 and a flexible end 44 comprising a finely coiled structure welded to the distal extremity of the wire body 42. The guide wire is steered and its flexible end is advanced into position within the target coronary vessel using a releasable or selectively lockable clamp 46 which, when loosened, can be slid along the wire body 42 of the guide wire.
In use, the guide wire 40 is inserted into the patient's vascular system utilizing an introducer. After the flexible end of the guide wire is properly placed, the introducer is withdrawn, the clamp 46 is removed and the lead is slid over the exposed part of the guide wire and advanced “over-the-wire” into the vessels. With the distal portion of the lead in place within the target vessel, the guide wire is withdrawn. In some instances, a sheath is first routed over the guide wire to protect the walls of the vessels along the insertion path. In these cases, after the sheath is in place, the guide wire is removed and a medical device such as a lead or a catheter may then be introduced into the patient's vascular system through the sheath.
Conventional guide wires of the type described impart a degree of curvature to the distal end of the lead so as to facilitate the advancement of the lead's distal end through the tortuous paths of a patient's vascular system. To this end, if an obstacle is encountered, the guide wire is withdrawn from the lead and is given a temporary bend or curve, and then reinserted in the lumen of the lead to further advance the lead. The process of withdrawing the guide wire, rebending it (or substituting a fresh guide wire therefor) and reinserting it is repeated until the lead tip has been advanced to the target location. This conventional lead placement technique has drawbacks. For example, the guide wire can only be deflected or bent in a single direction. More importantly, repeated removal and reinsertion of the guide wire increases the risk of infection and injury to the patient in addition to being time consuming.
As an aid to efficiently and safely routing guide wires through the tortuous vasculature of the coronary sinus region, there have been developed guide wires having distal end portions deflectable in at least one direction by means of an actuating handle at the proximal end of the guide wire. There continues to be a need, however, for improvements in steerable guide wires in terms of simplicity and the range of curvatures in the deflectable distal end portion of the guide wire.